Resonant reed encoder-decoder, channel selector circuits therefor and communication circuits using the same



G. PAPAlcoNoMou 3,350,686

SELECTOR C Oct. 31, 1967 IRCUITS RESONANT REED ENCODER-DECODER, CHANNEL AND COMMU T'HEREFOB NLCATION CIRCUITS USING THE SAME Filed March 19,

2 Sheets-Sheet 1 INVENTOR mv T NoMou 3,350,585 R-DECODER, CHANNEL SELECTOR CIRCUITS UNICATIQN CIRCUITS USING THE SAME 2 Sheets-Sheet z l G. PAPAIC() RESONANT REED ENCODE THEREFQR- AND COMM Filed March 19, 1963 1 Oct. 31, 1967v INVENTOR cfoeec Papa/:couonou ,Ll/5 @Tram/EVS United States Patent O This invention relates to resonant reed encoder-decoder devices, particularly multichannel reed devices, to channel selector circuits therefor, and to communication circuits utilizing same, however, the invention is not necessarily so limited.

An object of the present invention is to provide a new and improved resonant reed encoder-decoder device.

Another object of the present invention is to provide an improved contact element for use in such devices.

Another object of the present invention is to provide an improved Vibratory reed contact arrangement, wherein the contact for the vibratory reed may be used alternatively as a variable condenser with said reed or as a relay switch upon contact withsaid reed. Y

Still another object of the present invention is to provide a new and improved channel selector for use in association with multichannel resonant reed devices.

Still another object of the present invention is to provide a channel selector arrangement for use in association with multichannel reed devices, wherein the number of available channels is extended to utilization of channels based upon simultaneous operation of a plurality of reeds.

A further object of the present invention is to provide new and improved two-way communication circuits for use at a plurality of stations, wherein the new and improved encoder-decoder devices of the present invention are utilized for the initiation ofy selective call signals and for the selective receipt of call signals.

Other objects and advantages reside in the construction of parts, the combination thereof,` the method of manufacture and the mode of operation, as will become more apparent from the following description.

' In the drawings, FIGURE 1 is a plan view of a resonant reed device constructed in laccordance with the present invention.

FIGURE 2 is a reed device. f

FIGURE 3 is a circuit diagram illustrating a two-way communication circuit employing the device of FIGURES l and 2.

FIGURE 4 is a circuit diagram illustrating a modified circuit.

p Referring to the drawings in greater detail, the resonant reed device of FIGURES l and Zis assembled upon a bracket having spaced parallel supporting legs 10a and 10b. Supported on the leg 10a is an L-shapedferromagnetic member 12 having an upwardly directed flange 14V upon which is seated a solenoid coil 16, the flange 14 serving as a core piece for said coil. Mounted on the member 12 in spaced relation to the coil 16 is an axially magnetized cylindrical permanent magnet 18. One pole face of the magnet 18 contacts the ferromagnetic member 12. The other pole face of the magnet 18 supports a second and smaller L-shaped ferromagnetic member 20, having an upwardly directed flange 21 which is disposed in spaced parallel relation to the core piece 14.

Mounted on a leg 10b of the bracket 10 are a plurality of parallel reeds 22a, 22b, 22e and 22d of ferromagnetic material. These reeds are mounted in cantilever fashion on the leg 10b by wrapping the supported ends of the reeds in a folded sheet 24 of conductive material towhich pressure isA applied by means of screws 25 threaded into side elevational viewV kofthe resonant the leg 10b. As is commonly understood in the art, the reeds 22a, 22h, 22e` and 22d may be formed separately or may be cut from a single sheet of material in such fashion that the supported ends of the reeds are interconnected by an uncut portion of the material from which the reeds are formed. In accordance with the present construction, whether the reeds -are separately formed or interconnected, the reeds are all in common electrically by virtue of the conductive sheet 24 which contacts each of the reeds. Where required, the conductive sheet 24, or any conductive element in contact therewith, may be used as a terminal.

The several reeds 22a-22d have varying lengths, so as to resonate at varying frequencies. Where a predetermined resonant frequency is sought, the length 0f the reed may be adjusted in small increments, or the mass at the free end altered in small increments, so as to tune the reed to thefdesired resonant frequency.

As best illustrated in FIGURE 2, the mounting of the reeds is such that they overlie the flange 21 associated with one ,pole ofthe magnet 18 and the flange 14 associated with the other pole of the magnet 18, but are spaced therefrom. In suchrposition, the reeds partially complete a magnetic flux path forthe magnet 18, there being air gaps between each of the reeds and the flanges 14 and 21. In consequence of this construction, an axially directed magnetic field is set up in the reeds, i.e., the reeds are polarized.

Supported above the reeds are a plurality of contact elements 28a, 28b, 28C and 28d, there being'one Contact element positioned above each reed for contact therewith. These contact elements-are sandwiched between an insulator 32 and a non-conductive header 26, this sandwich being subjected to pressure from the screw element 25. In contrast to the mounting of the reeds, each of the contact elements 28a, 28b, 28C and 28d is electrically separate and each has a rearwardly projecting tab 30which serves as a terminal therefor. The insulator 32 precludes direct electrical contact between the rearward ends of the contacts 28a-28d and the assembly of reeds 22a-22d.

At its forward end, each of the contacts is bent downwardly and then rearwardly to form a plate portionr 34 and, at its extreme end, is again bent downwardly to form a-contact flange 36. The plate 34 is axially parallel to the .underlying reed; but occupies a plane slightly inclined to theneutral plane of the underlyingreed.

FIGURE 2 illustrates the reed'22a in its neutral Iplane,

`wherein no signal is passing through the coil v16."When an alternating current signal having the frequency to which the reed 22a is tuned passes'through the coil 16, the magnetic field generated by the coil alternately attracts andrepels the magnetically polarized `reed 22a, causing this reed to rise above,.then fall below its neutral plane. The amplitude of such vibratory movement is dependent upon the strength ofthe signal. When the signal is weak, the amplitude `vmay be insucient to cause the reed to strike its contact flange 36. However, there will be a cyclic variation. inthe separation between the plate 34 in the contact 28a and the reed 22a. Thus, at low amplitudes, the contact 28a and its reed 22a function as a variable condenser, suchk that vibratory movements of the reed 22a can be utilized in an appropriate electrical circuit.

Threaded in the header 26 is a :plurality of adjustment screws 38, there being one screw aligned above each of the reeds 22a-22d. These screws may be employed to move each of the contact elements 22a-48d downwardly to'establish a predetermined separati-on between the reeds and their respective contacts, whereupon a signal of predetermined voltage will excite a reed tuned to the fre- ,f quency of the signal to an amplitude sufcient to produce actual contact between the reed and its associated contact element. Where actual contact is made, a make an-d break switching function can be performed by the reed-contact palrs.

For this switching operation, it is desirable that the contact elements be so designed that vibration in the contact element itself is avoided and interference with normal resonant vibration of the reed is minimized. To this end, the contact flange 36 is positioned inwardly of the free end of the reed, i.e., relatively close to the xed end of the reed, where lthe vibration amplitude is necessarily small and displacement of the associated contact element, even with a signal overvoltage, will be correspondingly small. Also, the plate 34 is inclined away from the outer end of the reed to enable the outer end of the reed to fiex upwardly beyond the poin-t of contact with the flange 36 without interference from the plate 34. It is found that for an adequate clearance for reed flexure, while maintaining optimum capacitance between the reed and the plate 34, the plate should be inclined to a position where it is approximately parallel to the underlying reed when the -reed first contacts the fiange 36.

In the foregoing description, a reed device having four reed elements, each tuned to resonate at a different frequency, has been described. For convenience, the operating frequencies are sometimes referred to as operating channels. Accordingly, the reed device illustrated is sometimes designated a four-channel reed device. While four reeds have been illustrated an-d described, it is understood that the number of reeds or operating channels may be increased or diminished, depending upon the requirements of the circuit in which the reed device is to function.

In the past, reed devices of this general type, especially single reed units, have been employed variously as electromechanical filters, as frequency responsive relays, as signal encoders, signal decoders, and the like. Without intending to limit the fiel-ds of application for the improved reed device disclosed herein, FIGURES 3 and 4 have been included in the application to disclose novel applications of the reed device as an encoder-decoder device in two-way radio communication circuits.

Use of the citizens band of radio frequencies has increased substantially in recent years. Since there are only a limited number of carrier frequencies in the citizens band, the same carrier frequency must be assigned to numerous operators, with the result that in any given area of the country, a single carrier frequency will be shared by a number of users. For example, if the driver of a taxicab is utilizing a radio receiver to receive messages from his home office, he will, in the absence of s-ome exclusionary device, receive not only the messages intended for him and the messages dispatched to all of the cabs serving the same company, but will also receive all of the messages dispatched in the same area by other users of the same carrier frequency. The circuits of FIGURES 3 and 4 offer a means for calling a selected receiver station to signify that a message intended for that station is forthcoming, thereby enabling the individual attending the receiver station to leave the receiver oft at all times except when a message intended for him is forthcoming. Conversely, the subject circuit permit the attendant at a receiver station to selectively call his home offiice or another receiver station for the transmission of messages.

Turning attention to the circuit of FIGURE 3, this circuit includes an antenna 40 which is used both for the transmission and receipt of messages. As illustrated, signals received by the antenna 40 are conducted to a radio frequency amplifier and mixer, then to an intermediate frequency amplifier, then to a detector, then to an audio amplifier and modulator, from which the incoming signal may be conducted to a loud speaker 46. For the transmission of signals, an audible message delivered to a microphone 48 is conducted to a microphone preamplifier, then to the audio amplifier, the output of which is delivered by conductor 51 to a radio frequency output amplifier,

4 wherein a carrier frequency controlled in a crystal oscillator is modulated for transmission by the antenna 40.

The portions of the circuit thus far described will be recognized as comprising a conventional radio transmitter and receiver. The remaining portions of the circuit constitute a means by which the radio transmitter-receiver is adapted to initiate selective calls and to selectively receive calls directed thereto. To this end, the output of the audio amplifier and modulator is transmitted through a conductor 42 to a three position switch, identified as SW1. The three positions for this switch are identified as SC, representing a selective call position, R, representing a receive position, and SR, representing a selective receive position. Obviously, when the switch is in the R position, all signals received by the antenna 40 on the carrier frequency to which th-e receiver is tuned will reach the loud speaker.

In the circuit as illustrated, the switch SW1 is in the selective receive position, such that the signals received by the antenna 40 on the carrier frequency to which the receiver is tuned are conveyed in the conductor 44 to a relay switch element 47, normally in contact with a contact 50, whereby the incoming signals are transmitted on conductor 52 to one terminal of the coil 16 in the reed unit of FIGURE 1, the other terminal being grounded at 56. As a result, all incoming signals to which the receiver is tuned are impressed on the coil 16.

Whenever a tone signal having a frequency to which one of the reeds 22a-22d is tuned is received in the coil 16, the particular reed tuned thereto will commence resonant vibration. For the purposes of the present circuit, the gain in the audio amplifier and the separation between the various reed and their respective contact flanges 36 is preadjusted, so that the signal strength will be sufficient to cause the reed to resonate at an amplitude sufficient to phy-sically strike its contact flange 36. The present circuit utilizes this contact action to operate a switch -for connecting the loud speaker with the audio amplifier in response to preselected tone signals.

For this function, a switch SW2 having two positions, one of which is selective call (SC) and the other of which is selected receive (SR), is positioned in the selective receive position, so as to isolate the reeds 22a-22d from ground. As previously indicated, the reeds are all electrically in common, due to the presence of the conductive sheet 24 used in supporting the reeds. Another switch SW3 also having SC and SR positions, is placed in its SR position. For response to signals simultaneously resonating the reeds 22a and 22C, the two selector switches SW4 and SWS are rotated to the positions illustrated.

The function of the reeds 22a and 22C, when simultaneously vibrating, is to drive the grid of the triode VT1 positive, by intermittently connecting the grid to the positive terminal B-iof a direct current voltage supply. The B-lterminal is connected through a relay coil RY to the plate of the triode VT1 and, as shown, the cathode of VT1 is grounded. When the -grid of VT1 is driven positive through simultaneous operation of the reeds 22a and 22C, VT1 becomes conductive, whereby the relay coil RY is energized to pull the relay switch element 47 against the contact 88, placing the audio amplitier in communication with the speaker 46 through conductor 92. Thus, upon simultaneous resonant vibration of the reeds 22a and 22C, the ultimate objective is to pass the audio amplifier output to the speaker 46.

The construction of the circuit, wherein a positive bias is applied to the grid of VT1 upon simultaneous vibration of the reeds 22a and 22C is as follows. The B-lterminal of the power supply connects through resistor R1 and conductor 72 to a jumper 70, interconnecting the stator contacts 5 and 10 of the switch SW4. In the switch position illustrated, the stator contact 5 of SW4 engages a rotor contact 68 which is therefore positive. The rotor contact 68 engages stator contact 3, which, through conductor 64C, is in communication with the contact element 28c paired with the reed 22C. Accordingly, whenever a signal received by the antenna 40 has the frequency to which the reed 22e is tuned, this reed intermittently receives a positive pulse, due to contact of the reed the contact element 28C.

Since the reed 22a is in comman with the contact 22C, this reed also receives an intermittent positive pulse and, when this reed is also resonating, due to a simultaneously received signal of the proper frequency, this positive pulse is intermittently applied to its paired contact 28a. Through conductor 64a, the positive pulse is also applied to stator contact 1 of the selector switch SWS. In the position shown, stator contact 1 Yof SWS is engaged with rotor contact 78, which is in continuous engagement with stator Contact 8 of selector switch' SWS. Accordingly, a positive pulse is intermittently applied to stator contact 8 and, through conductor 80, switch SW3 in the SR position and conductor 82, the positive pulse is conducted to the resistor R2 which permits a'current ilow to ground. The current ow AthroughRZ develops a positive bia-s on the grid of VTI. f 1 l Capacitor C1 is placed across the `resistance R2, so that this capacitor charges each time the reeds 22a and *22C are in simultaneous contact with their respective contact elements 28, and discharges through resistor R2, so as to maintain the positive bias during the times when either one or both reeds are out of contact with their respective contact elements.

In the preferred embodiment, the selector switches SW4 and SWS are ganged together, so that their rotors rotate in unison. When the two rotors are advanced from the position illustrated one increment in the clockwise direction, the circuit is Iset for response only to simultaneous resonance of the reeds '28b and 28d, due .to simultaneous receipt ofsignals to which these reeds are tuned. In this case, the current path moves'from the jumper 70 through stator Contact 5 in switch SW4,

through rotor contact 68 and stator contact 4in the same switch, through conductor 64d to contact element 28d, through reed 22d to reed 22b, through conductor 64b to -stator contact 2 in the switch SWS, then through rotor contact 78 and stator contact 8 in switch SWS to the grid of VTl. In similar fashion, it can be shown that adjustment of the selector switches SW4 and SWS a second increment in the clockwise direction, sets thecircuit for response to simultaneous vibration of the reeds 2211 and 22C, in the next increment, simultaneous vibration of theV reeds 22C and 22d, in the fourth increment, simultaneous vibration of the reeds 22d and 22a, and then in the sixth increment, simultaneous vibration of the reeds 22a and 22b, the foregoing reed pairs representing all of the possible pair combinations availablev with four reeds.

In View of the foregoing remarks, it is apparent that the circuit `of FIGURE 2 utilizing the four-channel reed device illustrated can be used to serve six separate receiving stations, each of which can be turned on selectively for receipt of a massage by simultaneous transmission of the proper combination o-f tones;

The present circuit is designed for the initiation of proper tone signals, as well as response to selected tone signals. For initiating tone signals, all switches are positioned in the SC position. Thus, SW1 is moved to the selective call position to isolate the loud speaker 46. As will become more apparent in the following, this is merely a convenience factor to eliminate useless broadcast of the initiating tones through the loud speaker 46.

SW2 is placed in the selective call position to ground the reedsZZa-ZZd. SW3 is placed in a selective all position to remove any possibility of bias on the tube VTI and, as will become more apparent subsequently, to permit the transmission of each tone generated to the microphone preamplifier. At the same time, a switch SW6, not previously mentioned, is moved from its selective receiveV position to the selective call position;

In the selective receive position of SW6, which is the typical operating position for this switch, condenser C2 has been charged from the B+ terminal through resistance R3. IWhen SW6 is turned to the SC position, condenser C2 discharges through relay coil 16 producing a magnetic eld which simultaneously deilects each of the reeds 28a-28d, initiatingr a temporary resonant vibration of these reeds. For this operation, the strength of the pulse produced in the coil 16 is made suiciently weak that the several reeds 22a-22d will not actually touch their respective contact elements.

With SW3 in the selective call position, the positive bias of the B+ terminal is applied through resistancev R4, conductor 96 and conductor 80 to stator contact 8 of the switch SWS and ultimately to the contact element 28a paired with grounded reed 22a. Due to the varying capacitance Vbetween the reed 22a and its contact element 28a, which is now in communication with the B+ terminal, an alternating current is passed through resistance R4, creating a varying potential which is applied to the plate of condenser C4 in communication therewith through conductors 94 and 96. Through resistance R6 f and conductor 98, this varying potential is supplied to the mlcrophone preamplifier wherein the signal is amplified and transmitted through conductor 49 to the audio amplilier modulator and then through conductor 51 to the RF output, wherein the carrier frequency of the crystal oscillator is modulated to superimpose thereon the frequency at which the reed 22a is vibrating.' At the same time, a positive bias is being'supplied from the B+ terminal through resistance R1, conductor 72, jumper 70, the stator contact 5 of switch SW4, SW4 rotor contact 68, stator contact 3 of SW4 and conductor 64C to the contact element 28e paired with the reed 22C. Accordingly, vibration of reed 22C generates an alternating current passing through resistance R1, thereby applying an alternatingvoltage to condenser C3, which is relayed through resistance RS and the conductor 98 to the microphone preampliiier, Vsuch that the carrier wave is simultaneously modulated to superimpose thereon a ysignal having the frequency of resonant vibration of the reed 22C. The result is that a signal is transmitted by'the antenna 40 carrying smiultaneously the two frequencies determine-d by vibration of the reeds 22a and 22e.

While this` signal is obviously of short duration, i.e., a few seconds of vibration in the reeds, it is of sufficient duration to .transmity an audible tone to a comparable transmitter-receiver unit set to the selective receive position Aand tuned to respond to the frequencies generated bythe reeds 22a and 22e. The attendant at such station, upon hearing the audible tone, can then switch his set Vto the receive positiony to receive messages spoken into the microphone 48 at the transmitting station.

Obviously, by adjustment of the selector switches SW4 and SWS, six different pairs of selective tones can be initiated for selectively initiating a call to six different receiver stations. In a typical operation, the circuit of FIGURE 3 accommodates siX different transmitter-receiver units, each of which can selectively call the other five and each of` which can selectively receive tone signals from the other ve. It is deemed withinV the purview of the present invention to increase or decrease the number of selections by an adjustment in the number of -reeds or channels and a corresponding adjustment of the selector switches SW4 and SWS.

It is to'be noted that the circuit of FIGURE 3 offers a distinct safety advantage, in that two simultaneously transmitted tone signals of the proper frequency are required for response at a receiver station. Accordingly, the probability of spurious switching at the receiver station is drastically reduced.

It will be apparent to those skilled in the art that the selective call operation of thepresent circuit can be employed to energize a light or buzzer or other signal device inaddition toor in llieu' of the loud speaker at the selected receiver station. Thus, FIGURE 4 illustrates a switch element 90 responsive to the relay RY which, upon energization of the relay, engages a contact 91 and can thereby close a circuit to a signalling device for indicating a forthcoming message.

The circuit of FIGURE 4 is a modification of the circuit of FIGURE 3 and illust-rates the use of single tone call signals, as opposed to the paired tone call signals of the circuit of FIGURE 3. This circuit also illustrates the use of an electrical oscillator for generating the call signals.

As with the circuit previously described, the present circuit discloses a type of accessory to a conventional radio transceiver. For conventional receiver operation, the switch SW7 is placed in the R (receive) position and incoming signals received in the antenna 100 are amplified in an RF amplifier and mixer, the output of which is delivered to an intermediate frequency amplifier, then to a detector, followed by an audio amplifier and modulator, then to a loud speaker 102. For transmission, audible signals spoken into a microphone 104 are amplied in the microphone preamplifier, transmitted through conductor 106 to the audio amplifier and modulator, then transmitted through conductor 108 to an RF output amplier, wherein a carrier wave controlled by the crystal oscillator is modulated for transmission by the antenna 100.

For selective receipt of tone signals, incoming signals are intercepted at the detector and delivered through conductor 110 to a contact 112 normally engaged by relay switch element 114. Switch element 114 is in communication with one plate of the capacitor C5 through conductor 116 and transmission of the incoming signal to this capacitor results in a variable voltage drop through the resistor R7, `representative of the incoming signals.

With the switch SWS in the SR position, the varying voltage developed in the resistor R7 is applied to the grid of the pentode VT2 through the conductor 122. The plate of VT?. is in communication with the positive B+ terminal of a direct current voltage supply through resistors R8 and R9, the cathode and suppressor screen being in communication with the negative terminal or ground. Positive bias is applied to the control screen through the resistors R10 and R11, with the capacitor C6-serving as a screen by-pass.

The amplified signal at the plate of VT2 is transmitted to the grid of the triode VT3 through the blocking capacitor C7, the capacitor C8 serving as -a decoupling capacitor. The plate of VT3 is in direct communication with the B+ power supply and the cathode in communication with ground through the resistances R13 and R14. Signal voltage at the grid of VT3 is ldeveloped across the resistances R12 and R13.

The amplified output of VTS is taken off the cathode through the capacitor vC9 and applied to one terminal of the reed energizing coil 16 through the conductor 130. The other terminal of this coil is grounded through the conductor 132.

Whenever a frequency signal is applied to the coil 16, -to which one of the reeds 22a-22d is tuned, such reed `will commence vibration. As was the case in the circuit previously described, the separation between the various reeds and their -respective contact elements 28a28d is adjusted in relation to the signal amplitude applied to the coil 16 to produce actual contact between the resonating reed and its contact element when the applied signal is externally received. The intermittent contact established between the resonating reed and its contact element is utilized to apply a positive bias to the grid of VT4, which, when conducting, energizes the coil of the relay RY. To this end, the switch SW9 in the selective receive position places the reeds 22a-22d in contact with the grid of VT4 through the conductor 133.

The plate of VT4 is in series communication with the coil for relay RY and the B+ terminal through the conductors 134 and 136. The cathode of VT4 is grounded through the conductor 138. Accordingly, when VT4 conducts, the relay coil is energized, drawing the -relay switch element 114 against the contact 140, interrupting the contact between the detector and the signal input capacitor C5 previously established by this switch element. At the same time, a second switch element 142 is moved `from an open contact 144 to a contact 146, whereby the output of the audio amplier modulator is conveyed directly to the loud speaker 102 through the switch SW7 and conductors 14S and 150. Thus, application of a positive bias to the grid of VT4 results in a transmission of all incoming signals received by the antenna to the loud speaker 102.

The positive bias Afor the triode VT4 is obtained in the following manner utilizing the selector switch SW10. Positive potential from the B+ terminal is applied to the stator contact 2 of the selector switch SW10 through conductor 118, resistance R8, conductor 154, resistance R15, conductor 156, and conductor 157. Stator contact 2 is in continuous communication with rotor contact 159 for the switch SW10 which, in the position illustrated, engages stator contact 6. The positive potential thereby applied to stator contact 6 is transmitted to the contact element 28d for the reed 22d through conductor 158. When the reed 22d is resonating, so as to intermittently contact its contact element 28d, intermittent positive bias is yapplied to the grid of VT4 through the conductor 133. At the same time, capacitor C10 is charged. As soon as VT4 has become conductive, the relay RY interrupts the signal supplied to the pentode VT2 and, accordingly, interrupts application of the incoming tone signal to the reed coil 16. As a result, the source of positive bias on the triode VT4 is interrupted. However, at this time, the capacitor C10 discharges through the resistance R16, maintaining the positive bias on the triode VT4 for a reasonable period of time, which might be several seconds.

By maintaining the positive bias on the grid of VT4, the output of the audio modulator is applied to the loud speaker 102 `for a sufficient period of time to produce a clearly audible tone signal in the loud speaker 102.

In the preceding remarks, the circuit of FIGURE 4 has been discussed with reference to operation as a selective `receiver when the selector switch SW10 has been set to cause the receiver to respond only to an incoming signal having the frequency to which the reed 22d is tuned. If the switch SW10 is rotated one increment in the clockwise direction, positive voltage is applied to the stator contact 7 and through the conductor 160 to the contact element 28C. Accordingly, in this position, the receiver responds only to signals to which the reed 22C is tuned. Movement of the rotor for SW10 a further increment in the clockwise direction places the positive voltage on the stator contact 8 and through the conductor 162 on the contact element 28b, and in this position the receiver responds only to signals having a frequency to which the reed 22b is tuned. Rotation of the rotor of SW10 a further increment in the clockwise direction places the positive potential on the stator contact 1 and, through the conductor 164, this potential is applied to the contact element 28a, whereupon the receiver is responsive only to incoming signals having a frequency to which the reed 22a is tuned.

From the foregoing, it is apparent that the receiver of FIGURE 3 can be set for selective receipt of four different tone signals represented by the four reeds 22a-22d. In some instances, it is desired to set a receiving station for receipt of any one of the four tone signals. For this purpose, the selector switch SW11 is included in the circuit. It is believed -obvious from an inspection of this switch that When the rotor contact 161 for this switch has been rotated one increment in a counterclockwise direction from the position illustrated, the positive potential applied to the stator contact 2 of this switch is simultaneously applied to each of the stator contacts 6, 7, 8 and 9 1. Accordingly,in this position of the switch SW11, any tone signal having the frequency of any one ofthe four reeds will be capable of connecting-theloud speaker 102 to the audio amplifier, effectively turning the receiver on.

It will be noted that the selector switches SW and SW11 are designed for unison operation .through five switch positions, four for selective response to any one of four individual tone signals and the fifth for nonselective response to all of thetone signals.

The present circuit is used to generate selective call signals in the following manner. Switches SW7, SW8 and SW9 are each moved to the selectivecall (SC) position. The selective call position for SW1 is merely a convenience to prevent needless broadcast of the call signals through the loud speaker `102 at the initiating station. When the switch SWS is moved to the call position, positive potential from the `B| terminal is applied to one plate-of the ycapacit-or C11 through the 4resistances R8 and R15. This positive pulse draws current through resistances R17 and R18, inducing a positive pulse on the grid of the pentode VT2. This pulse is amplified through VT2 and VT3 and then applied to the reed coil 16, causing each of the reeds 22a-22d to deflect.

This deflection of the reeds, while insufficient to produce contact with the contact elements 28a-28d, initiates a resonant vibration in the reeds. Through positioning of the switch SW9 in the selective call position, each of the reeds is grounded through the conductor 132. With the selector switches SW10 and SW11 in the positions indicated, the contact element 28d is in communication with the B-I- terminal through the resistances R8 and R15. The vibratory capacitance effect between the reed 22d and its contact element 28d therefore induces a pulsating current iiow through the resistance R15, which is transmitted through the condenser C11 to the grid of VT2. This 4pulsating signal is amplified in VT2 and VTS, then applied to the reed coil 16, whereby regenerative vibration of the reed 22d is established.

In the absence of some limiting factor on the strength of the regenerative tone signal developed in the reed coil 16, vibration of the reed 22d would build up until the reed repeatedly struck the contact element 28d with a violent destructive force. For limiting the strength of this tone signal, the amplifier based on the tubes VT2 and VT3 is equipped with an automatic gain control.

This gain control comprises a diode D1, which -grounds negative portions of the signal passed from the condenser C9 to the reed coil 16 through resistor R18, at the same time charging the condenser C12. Subsequent discharge of the condenser C12 through the resistance R18 establishes a persisting negative potential at the resistance R18, which is applied to the grid of VT2 through the conductor 168 and the resistance R17. The stronger the signal passed through the condenser C9, the stronger the negathe regenerative signals applied to the coil 16 is suptive bias applied to the grid of VT2, the result being that pressed to a reasonable operating level. Using techniques well understood in the art, the gain control is adjusted to limit the regenerative signal to a level below that required to establish contact :between the reeds and their respective contact elements 28a-28d.

It is believed apparent that the frequency of the regenerative tone signal developed for selective calling may be set to correspond to the resonant frequency of any one of the reeds 22a22d by adjustment of theswitch SW10. For transmission of the selected tone signal, the signal is passed to ground through conductor 170 and the resistance R19. A divided portion of this signal, selected by an adjustable tap on the resistance R19, is transmitted through the conductor 172 to the audio amplifier and modulator, and the output of the audio amplifier and modulator is transmitted to the radio frequency output amplifier through the conductor 108, wherein the carrier wave controlled by the crystal oscillator is modulated by the tone signal for transmission by the antenna 100.

From the foregoing remarks, it is clear that the circuit of FIGURE 4 can be used alternatively to selec- .tively receive tone signals while the loud speaker 102 is -mote receiver stations tuned to respond to the selected tone signals.

In the foregoing, two circuits especially adapted for use with the novel reed device disclosed herein have been discussed. Both circuits offer the advantage that a plurality ofreceiver sations, comprising a type of closed network, may be left with their speakers normally deenergized,1i.e., turned off, -but may each be turned on remotely on a selectivebasis to announce a forthcoming message. Further, both circuits also provide for the transmission of selected tone signals for selectively calling other receiver stations in the same network.

While the circuit of FIGURE 3 utilizes simple mechanically produced tone signals which are attenuated with time, and selector switch circuitry to produce paired tone signals and the circuit of FIGURE 4 uses amplified regenerative tone signals and associated selector switch circuitry to produce single tone signals, it will be apparent to those skilled in the art that these features are interchangeable. It will further be apparent to those skilled in the art that the selective call and receive circuitry employed herein can be extended logically to cover various combinations of simultaneous tone signals, such as triplets, and also to successive tone signals without the exercise of invention.

Although the preferred embodiment of the device has been described, it will be understood that within the purview of this invention various changes may be made in the form, details, proportion and arrangement of parts, the combination thereof, and mode of operation, which generally stated consist in a device capable -of carrying out the objects set forth, as disclosed and defined in the appended claims.

Having thus described my invention, I claim:

1. A selective frequency signal generator comprising, in combination, a resonant reed device having an energizing coil ,and a first group of ferromagnetic vibratory reeds tuned to separate resonant frequencies responsive to the magnetic field of said coil, a second group of conductive plate elements paired with said reeds for sensing vibratory movements of said reeds, there being one plate element for each reed, means mounting said plate elements adjacent their respective reeds, a first conductor electrically connecting the members of one of said groups and forming a first terminal, a plurality of second conductors, there being one second conductor connected electrically to each member of the other of said groups, a second terminal, and selector switch means to selectively connect any one of said second conductors to said second terminal whereby the reed-plate pair selected by said switch represents a variable capacitor across said terminals upon vibration of the selected reed, means to pass a current pulse through said coil effective to vibrate all of said reeds, and means responsive to the variable capacitance at said first and second terminals to produce an alternating voltage signal the frequency of which corresponds to the resonant frequency of the selected reed.

2. The selective frequency signal generator according to claim 1, wherein the means to pass a current pulse through said coil includes an amplifier having -an input and an output, means to impress the output of said arnplifier on said coil, means to initiate a pulse in said amplifier 'whereby said reeds are induced to vibrate so as to produce a variable capacitance at said first and second terminals, a direct current voltage supply and resistive load in series with said first and second terminals whereby the variable capacitance at said terminals induces a Variable voltage at one of said terminals, means coupling said one terminal to the input of said amplifier to thereby produce a regenerative signal having the frequency of the selected reed-contact pair in said coil, and means to limit the gain of said amplifier so as to maintain the amplitude of vibration in the selected reed below a predetermined amplitude.

3. A selective frequency resonant relay responsive to simultaneously received multiple frequency signals comprising, in combination, an energizing coil, a first group of ferromagnetic reeds tuned to separate resonant frequencies and responsive to the magnetic field of said coil, a second group of conductive Contact elements paired with said reeds for sensing vibratory movements of said reeds, there being one contact element for each reed and cooperating with such reed to form a reed-contact pair, means mounting said contact element adjacent their respective reeds for contact therewith upon vibration thereof at a predetermined amplitude, a first conductor electrically connecting the members of one of said groups, a plurality of second conductors, there being one second conductor connected electrically to each member of said other group, a first terminal, rst selector switch means to selectively connect any one of said second conductors to said first terminal, a second terminal, and second selector switch means to selectively connect any one of said second conductors to said second terminal whereby upon selection of different reed-contact pairs by said selector switch means and simultaneous vibration of the reed-contact pairs selected an intermittent short circuit is produced between said first and second terminals.

4. The relay according to claim 3, including means interconnecting said first and second selector switch means for unison operation thereof, said switch means being interconnected to move in unison through a plurality of positions in each of which a different pair of reed-contact pairs is selected by said switch means.

References Cited UNITED STATES PATENTS 3,033,955 5/1962 Monda et al. 200-9L3 3,138,745 6/1964 Slater et al. 20G- 91.3 3,240,898 3/1966 Fisher 20D-91 NEIL C. READ, Primary Examiner. P. XIARHOS, D. YUSKO, Assllstan Examiners. 

3. A SELECTIVE FREQUENCY RESONANT RELAY RESPONSIVE TO SIMULTANEOUSLY RECEIVED MULTIPLE FREQUENCY SIGNALS COMPRISING, IN COMBINATION, AN ENERGIZING COIL, A FIRST GROUP OF FERROMAGNETIC REEDS TUNED TO SEPARATE RESONANT FREQUENCIES AND RESPONSIVE TO THE MAGNETIC FIELD OF SAID COIL, A SECOND GROUP OF CONDUCTIVE CONTACT ELEMENTS PAIRED WITH SAID REEDS FOR SENSING VIBRATORY MOVEMENTS OF SAID REEDS, THERE BEING ONE CONTACT ELEMENT FOR EACH REED AND COOPERATING WITH SUCH REED TO FORM A REED-CONTACT PAIR, MEANS MOUNTING SAID CONTACT ELEMENT ADJACENT THEIR RESPECTIVE REEDS FOR CONTACT THEREWITH UPON VIBRATION THEREOF AT A PREDETERMINED AMPLITUDE, A FIRST CONDUCTOR ELECTRICALLY CONNECTING THE MEMBERS OF ONE OF SAID GROUPS, A PLURALITY OF SECOND CONDUCTORS, THERE BEING ONE SECOND CONDUCTOR CONNECTED ELECTRICALLY TO EACH MEMBER OF SAID OTHER GROUP, 